A hybrid vehicle may recover and store a vehicle's kinetic energy during conditions where driver demand torque is low. Specifically, the vehicle's kinetic energy may be converted into electrical energy that is stored in an electric energy storage device. The stored electrical energy may be utilized at a later time to accelerate the vehicle so that the vehicle consumes less hydrocarbon based fuel. The electric machine may also provide vehicle braking when the vehicle's kinetic energy is regenerated into electric energy via producing and applying a negative torque to the hybrid vehicle's driveline. In series hybrid vehicles that include a driveline disconnect clutch, the disconnect clutch and electric machine may increase driveline inertia such that a driver may notice a driveline torque disturbance during transmission shifting while the vehicle is in a regenerative braking mode.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for operating a driveline, comprising: adjusting torque output of an electric machine during a torque transfer phase of a transmission shift from a first fixed gear ratio to a second fixed gear ratio while the electric machine is providing regenerative braking to the driveline.
By reducing an amount of negative torque applied to a driveline via an electric machine during regenerative braking and downshifting from a higher gear to a lower gear, it may be possible to provide the technical result of reducing driveline torque disturbances. Reducing negative torque output of the electric machine allows transmission output torque to gradually transition to a lower level instead of abruptly decreasing as transmission clutches are simultaneously applied and released. For example, the electric machine negative torque may be reduced during a torque transfer phase of the downshift. Additionally, in some examples, electric machine negative torque may be further reduced during an inertia phase of the downshift.
The present description may provide several advantages. In particular, the approach may reduce driveline torque disturbances. Reducing driveline torque disturbances may include reducing torque holes where transmission output torque may be reduced more than desired. Further, the approach may be combined with other driveline torque smoothing techniques to improve vehicle drivability.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.